1. Field of the Invention
The present invention relates to manufacturing of a semiconductor device and it particularly relates to a method and an apparatus for forming a polycrystal silicon film on a capacitor electrode surface.
2. Description of the Related Art
As semiconductor devices become more highly integrated in recent years, further reduction in cell size is demanded. Particularly, in the case of dynamic random access memory (DRAM) in which one transistor and one capacitor make up one bit, if cell size is reduced, capacitor electrode size also diminishes, leading to a decline in data storage time. Additionally, if cell size diminishes, the capacity value falls and it becomes difficult to secure the minimum capacity to prevent memory data loss caused by an alpha ray and other factors.
As a method of reducing cell size and at the same time increasing capacitor electrode size, capacitors with a three dimensional structure such as a cylinder structure (FIG. 1(a)) and a fin structure (FIG. 1(b)) were devised and put into practice. These methods, however, have limitations. Additionally, to increase a capacity value, forming a thin film such as tantalum oxide (Ta2O5) (FIG. 1(c)) with high dielectric constant or barium titanic acid strontium (Ba(x)Sr(1xe2x88x92x)TiO2) (FIG. 1(d)), a ferroelectric film, etc. on a silicon thick film stack surface has been discussed but has not yet been put into practice.
For that reason, the HSG process (hemispherical grained process) which increases a surface area by making Si of capacitor electrode surface uneven attracts attention. This process forms an amorphous silicon/polysilicon mixed-phase thin film selectively only on the active layer of an amorphous silicon surface and anneals the surface at approximately 560xc2x0 C. (1040xc2x0 F.). With polysilicon on the surface functioning as a nucleus, amorphous in the mixed-phase active layer then migrates, polycrystal crystallizes and polysilicon grains form. As a result, an uneven-shaped polysilicon film (HSG) is formed on the surface of an amorphous silicon electrode (FIG. 1 (e)).
When this HSG process is used, however, a problem occurs wherein phosphorus concentration in HSG grain decreases because doped phosphorus atoms (P) migrate poorly as compared with silicon (Si) when the foundation amorphous silicon migrates occurs. As a result, if a C-V measurement is performed, capacity decreases (is depleted) on the negative voltage side. Additionally, a Cmin/Cmax ratio worsens to 0.85xcx9c0.40 which was the ratio before HSG formation.
For that reason, a conventional method of supplementing deficient phosphorus by doping PH3 using another device has been used. However, because a semiconductor substrate once contacting the atmosphere needs to be rinsed before PH3 annealing, there were problems such as an increase in the number of processes and a decrease in a surface area due to the etched surface of HSG grain caused by re-rinsing.
Additionally, there was a problem which even if a semiconductor substrate is conveyed to a PH3 reactor without being rinsed, HSG migration progresses in a clean atmosphere and, in a batch method which processes multiple semiconductor substrates collectively, a discrepancy in the degree of migration in semiconductor substrates on the upper portion and lower portion of the boat occurs, and grain size changes.
Consequently, an object of the present invention is to provide a device for forming HSG with which the number of processes does not increase and a surface area does not drop.
Additionally, another object of the present invention is to provide a method of forming HSG with an even grain size at the upper and the lower portions of a boat without causing HSG migration to progress.
Furthermore, another object of the present invention is to provide a method and a device for manufacturing HSG which excels in stability and reproducibility.
To achieve the above-mentioned objects, a method and a device according to the present invention comprise the following processes and devices:
A method according to an embodiment of the present invention is for forming an HSG in a reactor, comprising: (i) removing a spontaneous oxidation layer formed on an amorphous silicon surface of a semiconductor substrate by preprocessing; (ii) dissociating hydrogen atoms from dangling bonds by heating the semiconductor substrate to a processing temperature; (iii) causing an amorphous silicon/polysilicon mixed-phase thin film to grow selectively and solely on an activated surface of the amorphous silicon surface in a silicon compound atmosphere; and (iv) continuously annealing the film to cause migration of the surface to form multiple projections and valleys on the surface. The method further comprises; (v) supplying a coupling compound such as a phosphorus compound (diluted with a dilution gas) to the reactor during a period of heating the semiconductor surface to a processing temperature; and (vi) annealing the semiconductor substrate in the atmosphere containing the coupling compound. In the above, steps (i) and (ii) can be modified or omitted as long as an amorphous silicon/polysilicon mixed-phase thin film is formed on a semiconductor substrate. In other words, in an embodiment, the method can be conducted from step
In the above, the silicon compound may include SiH4, Si2H6, and SiCl2H2. Further, the coupling compound is a compound capable of end-coupling the activated surface, which may include a phosphorus compound such as PH3. In an embodiment, the coupling compound at a concentration of approximately 0.5% to 2% may be supplied to the reactor at a rate of approximately 50 to 1000 sccm (preferably 100 to 500 sccm) during a heat-up period for annealing. In an embodiment, the final temperature for annealing may reach approximately 200xc2x0 C. to 750xc2x0 C. at a rate of approximately 10 to 30xc2x0 C./min., and during annealing, the pressure of the reactor may be approximately 1 to 10 Torr.
Specifically, in an embodiment, the dilution gas is either an inert gas such as nitrogen, argon, helium, etc. or hydrogen or a mixed gas of more than two kinds.
Further preferably, in an embodiment, a reactor which forms HSG and a reactor which anneals in the phosphorus compound atmosphere are independent, and a process which moves the semiconductor substrate without exposing it to the atmosphere between the two reactors is included.
An apparatus according to the present invention is used for conducting an HSG-forming method, wherein (i) a spontaneous oxidation layer formed on an amorphous silicon surface of a semiconductor substrate is removed by preprocessing; (ii) hydrogen atoms are dissociated from dangling bonds by heating the semiconductor substrate to a processing temperature; (iii) an amorphous silicon/polysilicon mixed-phase thin film is caused to grow selectively and solely on an activated surface of the amorphous silicon surface in a silicon compound atmosphere; (iv) continuously the film is annealed, thereby causing migration of the surface to form multiple projections and valleys on the surface; and (v) the surface is annealed in an atmosphere which contains a phosphorus compound and a dilution gas, thereby supplementing deficiency of phosphorus atoms.
The apparatus comprises: (a) a first reactor; (b) a first chamber with an elevating device connected to a lower portion of the first reactor; (c) a second reactor; (d) a second chamber with an elevating device connected to a lower portion of the second reactor; and (e) transferring devices connected to the respective chambers to transfer a semiconductor substrate from the first chamber and the second chamber, said transferring devices transferring the semiconductor substrate from the first chamber to the second chamber without exposing the semiconductor substrate to the atmosphere.
Preferably, in an embodiment, a gate valve is provided respectively between the transferring device and the first chamber and between the transferring device and the second chamber.
For purposes of summarizing the invention and the advantages achieved over the prior art, certain objects and advantages of the invention have been described above. Of course, it is to be understood that not necessarily all such objects or advantages may be achieved in accordance with any particular embodiment of the invention. Thus, for example, those skilled in the art will recognize that the invention may be embodied or carried out in a manner that achieves or optimizes one advantage or group of advantages as taught herein without necessarily achieving other objects or advantages as may be taught or suggested herein.
Further aspects, features and advantages of the present invention will become apparent from the detailed description of the preferred embodiments which follow.